Development of an impedance-based sensor for the detection of catalyst coking in fuel-reforming systems

Abstract

A novel sensor for detecting the early stages of catalyst coking in fuel reforming systems has been developed. The sensor was manufactured by inkjet printing a colloidal suspension of ceramic powders to create thin (20 [mu]m) catalytic and conductive elements of the sensor. The catalytic elements are composed of a Ni-YSZ cermet. The Ni-YSZ cermet was prepared with a concentration below the percolation limit (20 vol%) of nickel, ensuring a low electrical conductivity. As coke forms on the catalyst material, the nickel nodules in the Ni-YSZ are connected by electrically conductive carbon and the conductivity of the catalyst material increases, indicating coke formation. Sensors were tested in a 1% ethylene environment to induce coking. The sensor showed a strong response to coking by producing a signal on the order of hundreds of millivolts. The mass of the coke load was determined to be below the detection limit of available thermogravimetric analyzers (TGA) (less than 10 [mu]g). The coke load was further examined with a field effect scanning electron microscope (FESEM) and was found to be primarily carbon nanobers. Carbon nanofibers 10-50nm in diameter connected nickel nodules in the sensors catalyst material resulting in the observed change in resistance. Sensors were also tested in a dry reforming environment (methane-carbon dioxide). A custom signal amplification circuit was constructed to connect the sensor to an Arduino UNO microcontroller. By interfacing the sensor to the microcontroller, the sensor was able to automatically shut down a carbon dioxide-methane reforming fuel stream when coking conditions were present.